The present invention relates to a carburetor for an internal combustion engine.
In FIG. 1, a conventional carburetor of an internal combustion engine is shown. In this carburetor, a float chamber 5 with a float 6 therein communicates with a fuel passage 9 via a jet 4. An air bleed 7 fitted with an emulsion tube 8 also communicates with this fuel passage 9. A nozzle 3 leads from this fuel passage 9 to a small venturi 2. This small venturi 2 is located within a larger venturi 1.
This kind of carburetor aims at producing a homogeneous mixture of air which is ejected from the air bleed 7 with the fuel from the jet 4, in order to produce a finely divided jet of fuel from the nozzle 3. This air emerges from the emulsion tube 8 as fine bubbles.
However, it is found to be a problem that the air bubbles leaving the holes in the emulsion tube are apt to grow, just before they become detached from the holes, larger than the holes themselves; and further they tend to amalgamate with one another. Thus, although the hole diameter may be about 0.5 mm bubbles of 0.7 mm in size, or even larger, occur. Also, the generation of air bubbles through the holes is intermittent. For these reasons, alternately over-rich and over-lean fuel appear at the nozzle 3, and the so-called "pulsation phenomenon" appears, whereby the stability of revolution speed of the engine is adversely affected, the quality of the exhaust gas suffers, the mixture control accuracy decreases, and the fuel economy drops.
As an aid to uniform mixing of the air and the fuel, it has been proposed in Japanese Utility Model Application No. 66433/76 to provide a heater to apply heat to the fuel with air bubbles before it comes out of the nozzle, thus partially gasifying it. However, this means a complicated carburetor of a radically new structure.
As an alternative, it has been proposed in Japanese Patent Application No. 50960/77 to provide a sponge-like porous member in the fuel nozzle passage of the carburetor, so as to break up the bubbles. However, this proposition is fraught with difficulty, because a sponge-like member presents high resistance to the flow of fuel. If, to combat this, the sponge-like member is made very thin, it becomes so weak that it breaks easily, and further its effect in breaking up the bubbles is diminished. It is extremely difficult to provide a sponge-like member which satisfies the contradictory demands made upon it, in a nozzle of the usual diameter of 3 to 5 mm.